The concept of Content Centric Network (CCN) has been proposed by PARC (Palo Alto Research Center) and is considered as a promising candidate architecture for the future Internet.
CCN architectures have been disclosed for instance in documents US20090288163, US20090287835, and US20090285209.
During CCN's operation, each content delivered in the network has a unique structured name. The nodes of the network declare their interest in some content by sending an Interest packet with the name of the wanted content to other nodes of the network. Upon the reception of Interest packet, a CCN node determines whether the content satisfying the interest is available. If so, the corresponding content is sent to the Interest packet owner. Otherwise, the Interest packet is marked as pending in the receiving node and forwarded to a second node in the network based on the interest. After receiving content from the second node in response to the forwarded Interest packet, the node un-marks the Interest packet as pending and sends the content to the Interest packet owner.
A CCN node routes a packet based on the action corresponding to the condition as specified in its routing policy. The longest name match policy is used for determining whether a structured name included in the Interest packet is within the namespace specified in the routing policy.
A CCN node comprises a routing table containing three main data structures: a base called FIB (Forwarding Information Base), a buffer memory called ContentStore, and a table called PIT (Pending Interest Table).
The FIB is used to forward Interest packets toward potential source(s) of matching data. It is similar to an IP (Internet Protocol) FIB except it allows for a list of outgoing faces rather than a single one. The term face is used to represent a node registered in the routing table. The ContentStore is similar as the buffer memory of an IP router. The PIT is used to keep track of Interest packets that have been forwarded upstream toward content source(s) so that returned data can be sent downstream to its requestor(s).
A user device asks for content by broadcasting an Interest packet. A node receiving the Interest packet and having data that satisfies it can respond with a Data packet containing data related to the content. Data packet is transmitted only in response to an Interest packet.
Based on the CCN architecture, PARC proposes a system called VoCCN for facilitating voice calls over CCN, where a CCN user can direct voice calls to another CCN user by expressing an interest.
FIG. 1. represents a network comprising four CCN routers A1 to A4, and two IP routers B1 and B2. A CCN router A1-A4 may create and update its routing table as explained below.
When a media repository M1 next to router A1 is announcing that it can serve Interests matching the prefix ‘/parc.com/media/art’, the router A1 hears this announcement and, in response, installs a local CCN FIB entry for the prefix ‘/parc.com/media/art’ pointing at the face M1 where it heard the announcement. Then, router A1 packages the prefix ‘/parc.com/media/art’ into IGP LSA which is flooded to all nodes of the network.
Router A3 receives the LSA and adds in its routing table FIB a prefix entry for ‘/parc.com/media/art’ pointing to the face A1, as represented in FIG. 1.
Then, when a repository M2 adjacent to router A2 announces prefixes ‘/parc.com/media’ and ‘/parc.com/media/art’, router A2 floods an IGP LSA for these two prefixes.
When receiving the LSA from router A2, the FIB of router A3 is updated to contain /parc.com/media’ pointing at face A2, and ‘/parc.com/media/art’ pointing to faces A1 and A2, as represented in FIG. 1.
Then, if a user device adjacent to router A3 expresses interest in index /parc.com/media/art/impressionisthistory.mp4, this interest will get forwarded to both routers A1 and A2, and routers A1 and A2 will each forward it to their adjacent repository M1, M2.
A CCN router generally updates its routing table by creating one routing entry in the PIT for each received Interest packet, and one routing entry in the FIB for each received Link-State Advertisement (LSA). As a consequence, there is sharp growth in the size of routing table, because the routing table has to contain a large number of routing entries. Hence, the CCN approach has to face the challenge of scalability in a practical system.
The invention will improve the situation.